This invention relates generally to methods of evaluating a process of mixing and placing a fluid for oil or gas wells and more particularly to a method of evaluating a cementing process for oil or gas wells.
During the creation of an oil or gas well, various mixtures are typically blended and pumped into the well. For example, a cement slurry of at least water and cement is mixed at the well and pumped into it such as for securing a casing or liner in the bore. As another example, a slurry of at least a base fluid and sand is mixed at the well and pumped into it as a fracturing fluid for hydraulically fracturing a subterranean formation and propping the created fractures open with the sand to facilitate oil or gas flow from the formation into the well. These, and other fluids such as acids, for example, are handled at well sites and placed in wells; however, only cement and the cementing process will be referred to throughout the remainder of this disclosure.
Historically, the ability to quantitatively evaluate the quality of a cementing operation has been limited. When the designing, mixing and placing of cement slurry downhole has been evaluated, it has typically involved using qualitative or semiquantitative design parameters, rules of thumb, inherently variable material and variations of mixing equipment with virtually undocumented performance characteristics. Causes of failure occurring during placement have historically been almost impossible to definitively analyze. When cement has been successfully placed, operators have resorted to indirect acoustic methods to evaluate the expected performance of the cement sheath. The major evaluation method has, however, remained based on qualitative or semiquantitative wellbore performance acceptability criteria. Although cementing has been used for over 70 years in the oil and gas industry, the overall cementing process has not been critically analyzed in a manner whereby causes or modes of failure could be usefully evaluated in a concise manner or whereby both individual and overall cementing process quality could be assured or improved in a consistent and quantitatively defined manner.
Aside from a basic desire to understand the cementing process more fully and to assure that a quality cementing process is being provided to customers, there is also the need for an improved method of evaluating and improving the cementing process for oil or gas wells due to national and international quality assurance standards that exist today. For example, in Europe companies may have to comply with standards such as the ISO 9000 series of the International Organization for Standardization. When these companies are service users, they may be required to use only quality service providers who also comply with such standards. Thus, there is the need for an improved method of evaluating a process of mixing and placing a fluid, such as a cement slurry, for oil or gas wells so that more effective quality assurance and improvement can be obtained and further whereby specific standards can be readily met.